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Mitigating Health Risks with Laboratory Fume Hoods (Part I) : Chemical Exposure

Safety is a very important aspect of laboratory activity.  Without it, daily undertakings can lead to injuries, severe health risks, and even death.  To reduce these risks, there are certain procedures, also called Good Laboratory Practices (GLP), that we should all follow in the laboratory as individuals and as a member of a group. 

When it comes to safety related to chemical handling, it is crucial to protect yourself from toxic fumes and other vapours, hence avoiding any inhalation of chemicals. This safety can only be accomplished with the systematic usage of laboratory fume hoods which is the only equipment nowadays guaranteeing user’s protection from inhalation of chemicals.  Different types of fume hoods are currently available as we can adopt whether a traditional ducted system (featuring exhaust pipe) or a ductless system (featuring filtration technology).  Regardless of the category of fume hood, any units should comply with safety requirements given by International Safety Standards in Europe, North America, and Asia.   Unfortunately, many fume hoods available on the market do not meet these safety requirements mainly due to manufacturer’s poor expertise about fume hood, due to the lack of test and certification before and after installation, and due to lack of understanding on how to use a fume hood safety by the chemists.

Therefore, it is fundamental for any laboratory manager and personnel to make the difference between good and bad fume hoods, or again between safe fume hood and risky fume hoods, and to discipline chemists to use the fume hoods properly.  Safety awareness in the laboratory starts with familiarising yourself with all equipments and proper procedures before using your fume hood.  Throughout this article, you’ll read much on the important of laboratory fume hoo and the related safety requirements that it must comply with.  Basically it will be able to answer this question : How do I know if my fume hood (or my future fume hood) is considered safe or not ?.

Safety and chemical exposure

Before going more into technical details with fume hoods, it’s necessary to have first a clear understanding about the current safety regulations set in place for chemical exposure.  To put it simply, what are the average chemical concentrations to which workers can be exposed at workplace ?

Inhaling chemical presents potential risks for your health after a certain level of exposure.  It can lead to health consequences about specific or several organs, weakens the immune system, affects the blood and bone marrow or even causes death.  These consequences can be seen at short and long term depending about the severity of the chemical exposure.   

In USA, laboratory personnel follows strict guidelines from the National Institute for Occupational Safety and Health (NIOSH), while similarly regulations in Malaysia are under the Occupational Safety and Health Act for Use and Standards of Exposure of Chemicals Hazardous to Health (USECHH. 2000). 

In order to ensure end-user’s safety, these organisations have determined a regulatory limit on the amount or concentration of a substance in the air. These limits, or allowable airborne concentrations, are known under the designation Permissible Exposure Limit (PEL). We can also find them under the name Threshold Limit Value (TLV) or Occupational Exposure Limit (OEL) depending of the said country.

What is PEL-TWA ?

PEL is not only a value expressing the average concentration of a particular chemical that an individual can inhale at workplace. They also need to be determined on a frame period of 8 hours per dain order to define the Permissible Exposure Limit Time Weighted Average (PEL-TWA). PELs-TWA are indicated in part per million (ppm) and their values vary from a chemical to another based on the toxicity and molar mass of the molecules. Thus, the lower is the PEL-TWA, the riskier will be the chemical. For example, formaldehyde, with a PEL-TWA of 0.75 ppm, is considered very toxic while ethanol has a low toxicity with a PEL- TWA of 1,000 ppm.

On safety matter, a person inhaling regularly concentrations higher than the PEL-TWA of chemicals at workplace will imply a health risk.  Indeed, the daily exposure to low volume of chemicals may not have immediate health consequences but it does on the long term.  Then, it is crucial for any individual to minimise their chemical exposure at a threshold value much below the PEL-TWAs, since PEL-TWA values are determined for one chemical only.    It does not take into consideration of possible accumulation with other chemical present in the same room, or even the potential mix of different chemicals which is the case in a chemistry laboratory. 

A chemistry laboratory is a unique working environment with the presence of many toxic products in the room resulting in the possible exposure of multiple chemicals at the same time.   Therefore, there is an accumulation of different concentration of chemicals in the laboratory that could be inhaled by the workers.  Besides, there is also the risk of reaction of different chemicals, named “cocktail effect”, which may result in very dangerous mixtures.  This mixtures may represent a much higher danger in terms of toxicity and be insidiously inhaled by the users.  Eventually, the accumulation and mixtures of chemicals can have dramatic health consequences for a chemist despite its low PEL-TWA values. 

That is the reason why International Standards (e.g. SEFA 9, ANSI AIHA Z9.5: 2003, NFX 15-211) agree to authorise a maximum exposure in the laboratory at a 1% of the PEL-TWA for each chemical, or one hundred times below the authorised values.   Hence, the accumulation of chemical and the “cocktail effect” are drastically minimised, which do not present anymore health threat to the chemists.  A concentration below 1% of the PEL-TWA of each chemical used in the laboratory room can definitely ensure end-user’s safety.   


▶︎ article continues in Part II

(This article is contributed by Teddy Pitiot, Erlab)